01 - In a mixing bowl, whisk together ube halaya, sweetened condensed milk, evaporated milk, heavy cream, and ube extract until a smooth, creamy consistency is achieved.
02 - In a saucepan, combine whole milk, heavy cream, and granulated sugar. Sprinkle gelatin powder or agar-agar over the mixture and allow to hydrate for 5 minutes. Warm gently over low heat, stirring continuously until the gelatin or agar-agar completely dissolves—do not allow it to boil. Add vanilla extract, remove from heat, and let the mixture cool slightly.
03 - Arrange a slice of sponge cake at the base of each serving glass. Spoon an ample amount of the ube mixture atop the cake, followed by a layer of the milk jelly. If there is capacity in your glassware, repeat the layering, ensuring the milk jelly forms the final top layer.
04 - Place assembled trifles in the refrigerator and chill for a minimum of 2 hours, allowing the jelly to firmly set.
05 - Before serving, crown each portion with whipped cream and, if desired, scatter fresh ube cubes or purple sprinkles for added visual appeal.